Drug-eluting implantable medical devices, such as stents, have become popular for their ability to perform their primary function, i.e., providing structural support to a body vessel, and their ability to medically treat the area in which they are implanted.
For example, drug-eluting stents have been used to prevent restenosis in coronary arteries. Drug-eluting stents may administer active agents (also referred to herein as drugs) such as anti-inflammatory compounds that block local invasion/activation of monocytes, thus preventing the secretion of growth factors that may trigger vascular smooth muscle cell (VSMC) proliferation and migration. Other potentially anti-restenotic compounds include antiproliferative agents, such as chemotherapeutics, which include rapamycin and paclitaxel. Other classes of drugs such as anti-thrombotics, anti-oxidants, platelet aggregation inhibitors and cytostatic agents have also been suggested for anti-restenotic use.
Drug-eluting implantable medical devices may be coated with a polymeric material which, in turn, is impregnated with an active agent or a combination of active agents. Once the medical device is implanted at a target location, the active agent(s) is released from the polymer for treatment of the local tissues. The active agent(s) is released by a process of diffusion through the polymer layer for biostable polymers, and/or as the polymer material degrades for biodegradable polymers.
Controlling the rate of elution of a drug from the drug impregnated polymeric material is generally based on the properties of the polymer material. However, at the conclusion of the elution process, the remaining polymer material in some instances has been linked to an adverse reaction with the vessel, possibly causing inflammation or a small but dangerous clot to form. Further, drug impregnated polymer coatings on exposed surfaces of medical devices may flake off or otherwise be damaged during delivery, thereby preventing the drug from reaching the target site. Still further, drug impregnated polymer coatings are limited in the quantity of the drug to be delivered by the amount of a drug that the polymer coating can carry and the size of the medical devices. Controlling the rate of elution using polymer coatings is also difficult.
Stents with hollow, drug-filled structural members have been contemplated and developed. For example, U.S. Pat. No. 6,071,305 to Brown et al., generally discloses a stent formed of an elongated member in a spiral tube configuration. The elongated member includes a groove that can be filled with an active agent. Further, U.S. Pat. No. 9,283,305 to Birdsall et al., U.S. Application Publication No. 2011/0070358 to Mauch et al., U.S. Pat. No. 8,460,745 to Mitchell et al., and U.S. Pat. No. 9,119,736 to Thompson, each of which is herein incorporated by reference in its entirety, describe methods of forming and filling stents with hollow, drug-filled structural members from composite wires. There remains a need in the art for improvements of drug-filled stents.